1. Field of the Invention
This invention relates generally to a system and method for detecting whether a vehicle is approaching a curve in the mad too fast, and if so, automatically providing braking control and, more particularly, to a system and method for determining whether a vehicle is approaching a curve in the mad too fast, and if so, automatically providing braking control, where the system and method adaptively determine when to provide curvature information of the curve based on vehicle speed and selectively provide driver aggressiveness control.
2. Discussion of the Related Art
Driving too fast on a road curve could cause not only discomfort for vehicle occupants, but also, under some circumstances, the loss of vehicle control. If a driver approaches a curve at too high of a speed, vehicle control prior to normal curve steering begins with a reduction in vehicle speed. The deceleration level required for a curve depends on many factors, such as the curvature of the road, the vehicle speed, the curve bank angle, the road gradient, the road surface coefficient of friction, vehicle characteristics, driver competence, etc. Usually, a driver relies on his or her visual information about the upcoming curve to determine the proper speed and braking level. Although there are generally warning signs for sharp curves, such as posted speed limits, drivers sometimes do not pay attention to these warning signs or follow the posted speed limit. The timing of the brake application relative to the vehicle's position on a curve is also important in that it is generally necessary to slow down enough before the vehicle reaches the curve. Failure to perform a proper maneuver may result in not only repeated adjustments of the brake and steering, but also, possibly serious accidents by crossing the lane boundary or going off the road.
Certain active safety techniques have been developed in the art that may assist drivers in maintaining vehicle control during cornering. The conventional implementations of the active safety approaches have been anti-lock braking and traction control systems to help drivers corner safely by sensing road conditions and intervening in the driver's brake and throttle control selections. However, drivers may be helped further by complimenting such control systems with strategies that intervene in vehicle control prior to entering a curve.
Through study and simulation, a smaller curve radius has been shown to require a larger steering input and steering error increases linearly with required steering wheel angle. Drivers compensate for this by choosing a slower speed, such that the time to line crossing to the inner boundary is constant over all curve radius. Thus, the safety margin to the inner lane boundaries are maintained.
One known system for determining whether a vehicle is approaching a curve too fast, and if so, automatically providing vehicle braking, is described in U.S. patent application Ser. No. 11/297,906, titled Speed Control Method for Vehicle Approaching and Traveling on a Curve, filed Dec. 9, 2005, assigned to the assignee of this application and herein incorporated by reference. This system uses GPS signals, a map database, vehicle speed, vehicle yaw rate and steering angle to provide a profile of the proper speed for a vehicle traveling around a curve at different distances from the vehicle.
This system has limitations in that the system is calibrated to provide road curvature information at a predetermined distance of the curve, such as 250 meters. As a result, the resolution of the curve data is limited because there are fixed steps between the data points, and the number of map points will be limited due to computation and communication time. Therefore, if a vehicle is traveling slowly, the curvature information provided at the fixed step increments a predetermined distance from the curve may not be necessary, and thus the resolution of the system may be limited. Further, if the vehicle is traveling at a high speed, the fixed distance from the curve to provide the curvature information may be too close to the curve to ensure a smooth deceleration before reaching the curve.